Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$115.31	10.571%	$127.4994	$127.50	$127.50	$127.50
Purchase #2	$23.77	7.257%	$25.495	$25.50	$25.50	$25.50
Purchase #3	$116.67	5.496%	$123.0822	$123.08	$123.10	$123.10
Purchase #4	$183.52	8.639%	$199.3743	$199.37	$199.35	$199.40
Purchase #5	$61.80	4.386%	$64.5105	$64.51	$64.50	$64.50
Purchase #6	$213.45	6.355%	$227.0147	$227.01	$227.00	$227.00
Purchase #7	$142.77	3.630%	$147.9526	$147.95	$147.95	$148.00
7 purchase totals =	$857.29		$914.9287	$914.92	$914.90	$915.00